1. Field of the Invention
This invention relates to linerless labels and, in particular, to linerless labels having pressure sensitive adhesive and release coatings.
2. Description of Related Art
Linerless labels, such as shown in U.S. Pat. Nos. 3,051,588, 3,285,771, and 4,851,383, and in Canadian Patent No. 1,248,412, are known to have advantages over conventional pressure sensitive labels that are mounted on a separate liner having a release coating. In conventional labels, the liner acts as a support for transport, printing and storage, and is discarded after the label is removed from the liner. In contrast, a linerless label has a face surface that is coated with a release coating and a back surface that is coated with a pressure sensitive adhesive (PSA). A strip of linerless labels may be wound in a roll configuration so that the PSA on the back side of the strip is in contact with the release coating on the face side of the strip, where the release coating faces outwardly. The adhesion between the PSA and release coating holds the strip in a roll. Labels can be peeled off individually from the roll of linerless labels, without having a liner web to tear off and discard each time a label is used.
Because a liner web is not needed in a roll of linerless labels, certain advantages and cost savings are realized, including substantial material reduction due to the lack of a liner, elimination of the disposable liner and costs associated with release coated liners, and space savings in that a roll of linerless labels can have about twice as many labels as a same size roll of labels with liners. Despite these advantages, linerless labels have not enjoyed widespread commercial acceptance. The lack of acceptance is perhaps due in part to impediments to easy and clean peeling of the PSA from the release coating in the roll format. For example, if the adhesion between the PSA and the label substrate is weak or becomes weak (adhesion strength degrades over time under some environmental conditions and with some materials), then the PSA adhesive may stick to the release coating instead of the label as is intended, or the substrate may be torn when the labels are peeled off the label roll.
Silicone release coatings have been proposed for use with linerless labels. It has been found, however, that while certain silicone release compositions provide adequate release properties for pressure sensitive adhesives, it is difficult to print on such coatings due to the low surface energy of silicone coated substrates.
Thus, the need exists for a release coating composition that provides adequate release properties for pressure sensitive adhesives, and also allows ink to transfer to the release surface, particularly for thermal transfer printing.
The present invention satisfies that need by providing a release composition and a linerless label incorporating that release composition that provide excellent release properties for a pressure sensitive adhesive while also providing good anchorage of ink to the release surface.